High‐temperature collisional energy transfer in highly vibrationally excited molecules II: Isotope effects in isopropyl bromide systems

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Abstract
Values for 〈ΔEdown〉, the average downward energy transferred from the reactant to the bath gas upon collision, have been obtained for highly vibrationally excited undeuterated and per‐deuterated isopropyl bromide with the bath gases Ne, Xe, C2H4, and C2D4, at ca. 870 K. The technique of pressure‐dependent very low‐pressure pyrolysis (VLPP) was used to obtain the data. For C3H7Br, the 〈ΔEdown〉 values (cm−1) are 490 (Ne), 540 (Xe), 820 (C2H4), and 740 (C2D4), and for C3D7Br, 440 (Ne), 570 (Xe), 730 (C2H4), and 810 (C2D4). The uncertainties in these values are ca. ±10%. The 〈ΔEdown〉 values for the inert bath gases Ne and Xe show excellent agreement with the theoretical predictions of the semi‐empirical biased random walk model for monatomic/substrate collisional energy exchange [J. Chem. Phys., 80, 5501 (1984)]. The relative effects of deuteration of the reactant molecule on 〈ΔEdown〉 also compare favorably with the predictions of this theoretical model. Extrapolated high‐pressure rate coefficients (s−1) for the thermal decomposition of reactant are 1013.6±0.3 exp(−200 ± 8 kJ mol−1/RT) for C3H7Br and 1013.9±0.3 exp(−207 ± 8 kJ mol±1/RT) for C3D7Br, which are consistent with previous studies and the expected isotope effect.

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